I. Field of the Invention
The present invention relates to wireless communication. More particularly, the present invention relates to method and apparatus for concurrently processing multiple calls in a spread spectrum communications system.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communication in which a large number of system users are present. Although other multiple access communication system techniques are known in the art, such as time division multiple access (e.g., TDMA and GSM), frequency division multiple access (FDMA), and AM modulation schemes such as amplitude companded single sideband (ACSSB), the spread spectrum modulation technique of CDMA has significant advantages over these other modulation techniques for multiple access communications systems. The use of CDMA techniques in a multiple access communications system is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,xe2x80x9d issued Feb. 13, 1990, and U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,xe2x80x9d issued Apr. 7, 1992, both assigned to the assignee of the present invention and incorporated herein by reference.
CDMA systems are typically designed to conform to one or more particular CDMA standards. Examples of such CDMA standards include the xe2x80x9cTIA/EIA/IS-95-A Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System,xe2x80x9d xe2x80x9cTIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systemxe2x80x9d (collectively, the IS-95 standard), the TIA/EIA/IS-98-A, -B, and -C standards entitled xe2x80x9cRecommended Minimum Performance Standard for Dual-Mode Spread Spectrum Cellular and PCS Mobile Stations,xe2x80x9d and xe2x80x9cThe cdma2000 standards for spread spectrum systems,xe2x80x9d (hereinafter, the IS-2000 standard). New standards are continually proposed and adopted for use.
Each of the standards noted above defines a mechanism for processing a single call between a mobile station and a base station. The mechanism is characterized by a call processing state machine on the signaling layer (i.e., layer-3) that includes a number of states and a set of allowed transitions between the states. Each state in the state machine corresponds to a particular state of the mobile station (or base station) with respect to the call being processed. A transition to a new state takes place upon the occurrence of certain specified events.
CDMA systems are originally designed to (primarily) provide voice communication. Consequently, the call processing state machine defined by the CDMA standards is designed to support a single call, which is typically a voice call. For systems that conform to a particular CDMA standard and designed to implement the call processing state machine defined by that standard, only one call can typically be processed at any given moment, and a new call cannot be processed until the active call is terminated. This one-call limitation restricts the type of services that can be provided to the user.
As modem day communication evolves, it is highly desirable to provide enhanced communications services beyond just voice-only or data-only communication. These enhanced services often rely on the ability of the system to concurrently support multiple calls. For example, the ability to concurrently transmit voice and video (e.g., via two concurrent calls) can be used to provide video conferencing. For some applications, it is desirable to allow for concurrent transmission of voice and data (e.g., transfer of a file while carrying on a conversation).
Thus, techniques that allow for the concurrent processing of multiple calls in a spread spectrum environment are highly desirable.
The present invention provides techniques that enable the processing of multiple calls in a spread spectrum communications system. The invention achieves this by modifying (or redefining) the call processing state machine defined by the CDMA standards (e.g., IS-95 and IS-2000) to include a (xe2x80x9ctraffic channelxe2x80x9d) substate indicative of the mobile station processing at least one active call. The invention further provides call control (CC) state machines of various types, which are used to control the processing of the associated calls. In an embodiment, one CC state machine is instantiated for each call to be processed, and the instantiated CC state machine is terminated upon the release of the associated call. Referring to FIG. 5, Layer 3 processing state machine refers to the overall state machine 500, and call control (CC) state machines refer to the voice, data, ISDN, and GSM state machine instantiated for each call.
An embodiment of the invention provides a method for processing one or more calls concurrently in a spread spectrum communications system. In accordance with the method, an indication of a particular call to be processed is received and a CC state machine for this call is instantiated. The instantiated CC state machine is identified with and used to control the processing of the particular call. Thereafter, one or more data transmissions related to the particular call are exchanged. Upon receiving an indication of an additional call to be processed, another CC state machine can be instantiated for the additional call. Correspondingly, upon receiving a directive to release a particular call, the call is released and its instantiated CC state machine is terminated. In an embodiment, each call to be processed is associated with a particular service option connection, which includes information indicative of a set of parameters (e.g., the physical channels) to be used for data transmission.
The instantiated CC state machine can be of a particular type selected based on the type of the call being processed. For example, different CC state machines can be used for voice, data, video, fax, ISDN, GSM, and other types of call. In one implementation, the instantiated CC state machine for a voice call includes: (1) a waiting for order substate indicative of a wait for an order from the base station, (2) a waiting for answer substate indicative of a wait for a user response to the particular call, (3) a conversation substate indicative of a period of permissible transmissions for the voice call, and (4) a release substate indicative of termination of the voice call.
Another embodiment of the invention provides a method for supporting two or more calls concurrently in a spread spectrum communications system. In accordance with this method, an indication of a first call (CallA) to be processed is received. A first service option connection (SO Conn1) to be used for data transmissions is determined, and a set of one or more physical channels is associated with the service option connection. The first call is mapped to the first service option connection, and a CC state machine is instantiated to control the processing of the first call. For each subsequent call to be processed, a separate CC state machine can be instantiated. Upon receiving a directive to release a particular call, the call is released and the instantiated CC state machine for that call is also terminated.
For the embodiments described above, when multiple, concurrent calls are being processed, one or more additional service option connections to be used for data transmission can be determined. Each active call is mapped to one of the service option connections. When a call is released, a determination is made as to whether the service option connection of the just released call is used by at least one active call. The service option connection is released if it is not used by at least one active call. Similarly, when a service option connection is released, a determination is made as to whether the physical channel(s) associated with the released service option connection are used by another service option connection. A physical channel is released if it is not used by at least one active service option connection.
Yet another embodiment of the invention provides a method for processing one or more calls in a spread spectrum communications system. In accordance with the method, a particular communications system is selected for use and a paging channel is monitored for an alert message of an incoming call. For each of the calls being processed, one or more physical channels are established for data transmission and a CC state machine is instantiated. Messages are then exchanged for the calls over the established physical channels. An indication to release a particular call is received and the instantiated CC state machine for the particular call is released in response to the received indication. Yet another embodiment of the invention provides a mobile unit that includes a controller coupled to a receiver unit and a transmitter unit. The receiver unit receives incoming messages and the transmitter unit transmits outgoing messages. The controller receives an indication of a particular call to be processed, instantiates a call control state machine for the particular call, and exchanges one or more messages related to the particular call via the receiver and transmitter units. The instantiated call control state machine is identified with, and used to control processing of, the particular call. The controller can further receive an indication of an additional call to be processed and can instantiate an additional call control state machine for the additional call. The controller can also receive a directive to release the particular call and thereafter releases the call control state machine for the particular call.